What’s an Acre-foot?

In the water world, water is commonly measured in acre-feet. But
what is an acre-foot? One acre-foot equals about 326,000 gallons,
or enough water to cover an acre of land, about the size of a
football field, one foot deep. An average California household
uses between one-half and one acre-foot of water per year for
indoor and outdoor use.

California receives about 193 million acre-feet of water each
year as precipitation (rain and snow), but there is great
variability between regions. Yearly precipitation on the North
Coast is about 90 inches but only 2 inches in Death Valley.

Much of this precipitation evaporates, leaving California with 78
million acre-feet in surface water supply (including Colorado
River and Klamath River supplies) in an average year. Of that
water: 28 million acre-feet to 35 million acre-feet are used by
agriculture; 7.9 million acre-feet are used by cities and
industries; and 26 million acre-feet are used for the
environment.